Estimating Risk of Low Radiation Doses
W Hendee1*, M O'Connor2*, E Calabrese3*, (1) Rochester, MN, (2) Mayo Clinic, Rochester, MN, (3) ,MO-F-103-1 Monday 4:30PM - 6:00PM Room: 103
Several articles in the medical literature over the past few years have predicted thousands of cancers and cancer deaths annually in the US population caused by radiation exposures from medical imaging. The predictions are derived from risk estimates in the National Academy of Sciences BEIR VII report. These risk estimates are highly speculative with wide confidence intervals, and the BEIR VII committee has warned against using them to estimate cancer risks to individuals or populations. They are based on risk models derived from the linear no-threshold hypothesis of radiation risk at low doses. This hypothesis is derived from studies in the 1920s and 30s of genetic mutations in x-irradiated Drosophila and has a history of controversy and conflict. It has been challenged by experiments at the cellular and animal levels as well as by data of cancer incidence in medically-, occupationally-, and environmentally-exposed individuals. The main source of data for the BEIR VII risk estimates are the survivors of the Japanese A-bomb explosions, a population greatly different from the US population that was exposed to radiation conditions greatly different from those of medical imaging. Even so, data from the Japanese studies frequently reveal a threshold dose for increased cancers in the irradiated populations. Collectively, the uncertainties in the derivation of the BEIR VII risk estimates, and the intrinsic speculative nature of the risk estimates themselves, cause predictions of cancers and cancer deaths to be more hypothetical than real in populations exposed to medical imaging. Several scientific organizations, including the Health Physics Society, American Association of Physicists in Medicine, the International Organization of Medical Physicists, the United Nations Scientific Committee on the Effects of Atomic Radiation, and the International Commission on Radiological Protection, have warned against making such predictions because of their speculative nature. Unfortunately, these hypothetical predictions of cancer risks are themselves a health risk, because they create anxiety in patients resulting in a reluctance to undergo medical imaging procedures prescribed for their benefit.
1. Understand the origin of cancer risk estimates in BEIR VII
2. Appreciate the limitations in applying Japanese health data to American patients
3. Be familiar with the history and limitations of the LNT model of radiation injury